A 1-acyl-3-arylindoline compound represented by the general formula (1) ##STR2## (wherein R.sup.1 represents an optionally substituted phenyl group or an aromatic heterocyclic group, R.sup.2 represents a hydrogen atom, a halogen atom, a lower alkyl group, a hydroxy group, a lower alkoxy group, a carbamoyl group, or a lower alkoxycarbonyl group, and R.sup.3 represents a group of the following formula) ##STR3## is a compound useful as the 5-HT.sub.3 receptor antagonist (PCT/JP94/01641), and is produced by the condensation reaction of a 3-arylindoline compound represented by the general formula (2) ##STR4## (wherein R.sup.1 and R.sup.2 have the same meanings as defined above) with a carboxylic acid compound represented by the general formula (3) EQU R.sup.3 --COOH
(wherein R.sup.3 has the same meaning as defined above) or a reactive derivative thereof.
As means to produce the 3-arylindoline compound (2), methods for reducing a 3-arylindole compound represented by the general formula (4) ##STR5## (wherein R.sup.1 and R.sup.2 have the same meanings as defined above) under strongly acidic conditions, namely a method for effecting the reduction catalytically in the presence of such an strongly electrophilic reagent as a mineral acid like hydrochloric acid, hydrofluobromic acid, or orthophosphoric acid or an organic acid (preferably glacial acetic acid, propionic acid, trifluoroacetic acid, or formic acid) in the presence of such a Lewis acid as boron trifluoride, aluminum trichloride, or zinc chloride and a strongly acidic chemical reduction system for effecting the reduction by the use of boron trifluoride/zinc dust/glacial acetic acid or zinc dust/hydrochloric acid, have been known (JP-A-52-12,162). These methods, however, are invariably unfit for the reduction of an indole compound which is unstable under acidic conditions and are barely capable of producing a 3-arylindoline compound in a yield in the neighborhood of 50%. Further, since the reactions used by the methods are carried out under strongly acidic conditions, they are liable to corrode pressure reaction vessels made of a metal, by-produce copiously a toxic zinc compound, and incur difficulty in enabling the reaction product to be refined by the separation of the zinc compound. These factors render infeasible the commercialization of these methods.
As concrete examples of the means to produce an optically active substance of a 1-acyl-3-arylindoline compound (1), a method which comprises condensing an optically active substance of a 3-arylindoline compound (2) with an optically active substance of a carboxylic acid compound (3), a method which comprises separating by column chromatography an epimer mixture obtained by the condensation of a 3-arylindoline compound (2) and a carboxylic acid compound (3), either of them is an optically active substance and the remainder a racemic substance, and a method which comprises condensing a 3-arylindoline compound (2) and a carboxylic acid compound (3), both of which are racemic substances, thereby forming a diastereomer mixture, separating this mixture by column chromatography, and then optically resolving the components as by means of fractional recrystallization may be cited. A need is felt for a method of production which has as few component steps as possible, excels in operational efficiency, and permits production in a high yield.